Method of making a tap



Dec. 4, 1934. F, JUDGE 1,982,738

METHOD OF MAKING A TAP Original Filed NOV. 30, 1931 2 Sheets-Sheet lIlllllllllllllIlll||llll|llll|lllll|llllllllillllllllllllllllllllllllllllllllll -IiiunlllllulnllnmmlillllllllllllllIlllllllllll 11IllIlllllllllllllllllllll! JWM Dec. 4,1934. JUDGE METHOD OF MAKING A TAP Original Filed Nov. 30, 1951 2Sheets-$heet 2 DIWA- Q Patented Dec. 4, 1934 UNITED, T TES P E T OFFICEI v 1} 1,982,738 I H v I Greenfield Tap '& Die Corporation,

Mass, a corporation Greenfield, of Massachusetts Original applicationNovember 30, 1931, Serial;

No. 578,038. Divided and this application Novernber 20,1933, Serial No'.698,868

4 Claims.

3 This application is a division of my; prior ap-:

plication filed November 30, 1931, Serial No;

This invention relates to taps having succes- 5 sive cutting teethoffset. axially on opposite sides of a reference helix line.

land of the tap are offset on one side of the helix line and all of theteeth onthe next successive land of the tap are offset on the oppositeside.

A tap having these defined characteristics is shown and described in myprior application Serial No. 555,951, filed August 8, 1931.

My present invention relates to an improved method of manufacturing suchtaps.

My invention further relates to certain ordered procedure which will behereinafter described and more particularlypointed out in the appendedclaims. 7

= A preferred form of apparatus adapted for carryi-ng out my improvedmethod is shown in the drawings, in which Fig. 1 is a plan view ofportions 'of a tap hobbing machine designed to produce my improved taps;

Fig. 2 isfa diagrammatic view illustrating the detail steps of themethod, and Fig. 3 is a detail view showing the application of myimproved method to the production of dies. Referring to Fig. 1, I haveshownportions of a tap hobbing machine including a spindle l0 rotatablein a bearing 11 and provided with a gear 12 and chuck or driver 13. Atap T is secured in the chuck 13 andthe opposite endof thetap may besupported on atail center 14. v 1

' A hob H is supported on a shaft or spindle 20,

rotatable in bearings 21 and 22 on a support 23 longitudinally slidablein guideways in a stand 24:.

The spindle 20and hob H may be rotated 'in any convenient manner, as byaflexibleshaft 25.

Thestand 24 maybe adjusted toward and from the work by any suitablemechanism, whereby a cut of the desired depth will be taken.

An arm 26 projects outward from one end of the slide or support 23 andhas a slot 28 to receive a stud 29 mounted in a lever 30. The lever 30swings abouta fixedpivot stud 31 and is provided with a cam roll 32positioned in the periph eral cam groove 33 of a cam 34, mounted on acountershaft35. The shaft 35 is provided with a gear '36 engaging thegear 12 previously described. These gears are preferably of the samesize, so that the cam 34 makes one revolution for each rotation of thetap T. ii The side walls of the cam groove 33 are disposed at a slighthelical angle relative-to the axis of the shaft 35, which anglecorresponds to the pitch of thedesired thread onthe tap T.

In the process of manufacture, the hob H is rotated at a suitablecutting speed andthe tap s T is simultaneously rotated at relativelyslow In the preferred form, all of the teeth on one.

speed. Consequently'the teethof the hob Hform a series of grooves in aselected land of the tap T and these grooves and the intervening teethare formed at the desired pitch angle by reason of the gradual axialadjustment or shifting of the hob, effected by the helical cam groove 33as the cam 34 rotates in unison with the rotation of the tap T., r r

The apparatus as thus far described may be used to produce ordinary tapsnot having my alternately offset teeth. l y I I In order to produce thisalternate offsetting of the teeth by the hobbing operation, I modify thecam groove 33 as indicated in Fig. 2. 1

The portion a,of the-cam groove is used for producing the teeth on theland 1., which teeth aregofiset to the left with reference to the helixline P, providing clearanceon the face a.

When the teeth on the land 1 have been hobbed and the hob is out ofcontact with the tap, the cam groove. is axially offset or shiftedslightly to the right, as indicated at b, thereby causing the teeth onthe land 2 to be offset to the right of the normal helix line P, withclearance as indicated at b. Thecam groove is then shifted back toproduce a portion 0 in helical alignment with the portion a previouslydescribed and this portion produces the teeth of the land 3, withclearance on the right-hand side as indicated at c.

The cam groove is then again offset or shifted to the right, asindicated at d, thereby producing the teeth of the land 4, withclearance ontheir left-hand faces as indicatedat d.

The cam groove 33 then drops, abruptly back to its original position,aftercompletion of the teeth on the land 4, and the parts are promptlyreturned to a relation where the cam roll 32 is again located in theinitial cam portion a.

I am thus able to produce the alternately offset teeth shown in my,,prior application, with all of the advantagesthereindescribed, by theuse of a thread hobbing machine-for regular taps. Consequently theproduction of myspecially offset taps requires no extra operations andinvolves no increased expense. e

The carrying out of my improved method is not necessarily dependent onthe use of the apparatus shown, as other mechanism may be used, or therelative axial movement of the hob or tap may be effected manually.Obviously, it is immaterial whether the hob or the tap is shifted, solong as relative axial movement occurs.

The method comprises first the provision of the blank for the tap T withthe shank and the lands such as 1, 2, 3 and 4 and with the ,interveningflutes, all of these parts being symmetrically formed around the centralaxis. Then with the same hob each land in turn is cut with the groovesforming the desired teeth. Preferably the grooves of each land will becut substantially simultaneously as shown and successive lands will beoperated on in succession. The teeth will preferably have their apexesformed as flat ends e extending along helical lines concentric aroundthe central axis, and the center lines of these apexes of one row ofteeth will be out of alignment with the center lines of the apexes ofeach adjacent row.

In Fig. 3, I have shown the relation of the parts for hobbing a die D bya hob H projecting into the opening in the die. Relative axial shiftingof the hob and die may be used to produce relatively offset teeth in thedie D in the same manner as in the production of taps as previouslydescribed.

The invention may be applied to the production of three-land taps byhobbing one land in a normal helix line, relatively shifting the hob andtap axially in one direction to cause the teeth of the next land to beoffset at one side of said normal helix line, and then relativelyshifting thehob and tap to cause the teeth of the third land to beoffset at the opposite side of the normal helix line. In this case, theaxial shift between the second and third lands may be the normal amountof shift used in two or four flute,

commonly about .003", while the shift between the first and secondlands, or between the third and first, will be only one-half as much.

' Having described my improved method or process and a form of apparatusby which the method may be carried out, I do not wish to be limited tothe details herein disclosed, otherwise than as set forth in the claims,but what I claim is:-- t t 1. The method of producing a thread cuttingdevice comprising providing an integral structure having a number oflands and intervening flutes alternating arounda'given axis, cuttingsimultaneously a series of grooves in one of said lands to form a-row ofteeth having apexes disposed along predeterminedhelical center linesextending around said axis, and then cutting simultaneously by meanshaving substantially identical cutting contours, a series of grooves inthe next adjacent land helically off-set with respect to the grooves ofthe first-mentioned land to form a row of teeth having the same contoursas the teeth of the preceding land'and apexes disposed alongpredetermined helical center lines extending around said axis andhelically out of alignment with the center lines ofthe apexes of theteeth of the preceding land. 7

2. The method of producing a thread cutting device comprising providingan integral structure having a number of lands and intervening flutesalternating around a given axis, cutting simultaneously a seriesofgrooves in one of said lands 01 to form a row of teeth having flat-endedapexes disposed along predetermined helical center lines extendingaround said axis, and then cutting simultaneously by means havingsubstantially identical cutting contours a series of grooves in the nextadjacent land helically offset with respect to the grooves of thefirst-mentioned land to form a row of teeth having the same contours asthe teeth of the preceding land and flat-ended apexes disposed alongpredetermined helical center lines extending around said axis andhelically out of alignment with the center lines of the apexes of theteeth of the preceding land.

3. The method of producing a thread cutting device comprising providingan integral structure having a number of lands and intervening flutesalternating around a given axis, cutting simultaneously a series ofgrooves in one of said lands to form a row of teeth having flat-endedapexes disposed along predetermined helical center lines extendingaround said axis, then cutting simultaneously by means havingsubstantially identical cutting contours a series of grooves in the nextadjacent land helically offset with respect to the grooves of thefirst-mentioned land to form a row of teeth having the same contours asthe teeth of the preceding landand fiat-ended apexes disposed alongpredetermined helical centerlines extending around said axis andhelically out of alignment with the center. lines of the apexesof theteeth of the preceding land, and then cutting simultaneously by meanshaving substantially identical cutting contours, a series of grooves inthe next following land helically offset with respect to the grooves ofthe preceding land to form a row of teeth having the same contours asthe teeth of the preceding land and flat-ended apexes disposed alongpredetermined center lines extending around said axis and helically outof alignment with the center lines of the apexes of the teeth of thepreceding land.

4. The method of producing a thread cutting device comprising providingan integral structure having a number of lands and intervening flutesalternating around a given axis, cutting simultaneously a series ofgrooves in one of said lands to form a row of teeth having flat-endedapexes disposed along predetermined helical center lines extendingaround said axis, then cutting simultaneously by means havingsubstantially identical cutting contours a series of grooves in the nextadjacent land helically offset with respect to the grooves of thefirst-mentioned land to form a row of teeth having the same contours asthe teeth of the preceding land and flat-ended apexes disposed alongpredetermined helical center lines extending around said axis andhelically out of alignment with the center lines of the apexes of theteeth of the preceding land, and then cutting simultaneously by meanshaving substantially identical cutting contours a series of grooves inthe next following land helically offset with respect to the grooves ofthe preceding land to form a row of teeth having the same contours asthe teeth of the preceding land and flat-ended apexes dis-. posed alongpredetermined center lines extending around said axis and helically outof alignment with the center lines of the apexes of the teeth of thepreceding land and in helical alignment with the center lines of theapexes of the teeth of the first-mentioned land.

FRANKLIN JUD E.

